Well, the first thing I'd like to say is, Lanturn is in Gen 5 RU, which is not that very far away from OU, although still lower. Now, for the classic pros and cons.
1. Amazing 125 HP stat and decent SpD stat.
2. Access to both Thunder Wave to cripple opponents and Toxic.
3. Its high HP combined with decent SpD makes it a nice support, as it has access to Heal Bell too.
4. Scald is STAB and burns opponents while Volt Switch to pivot out.
5. The ability Volt Absorb, meaning it could just switch into checks like Magnezone or Jolteon.
1. Low defenses, and also low attack stat, sooo, the player using Sucker Punch might be a noob like me or used it for certain reasons.
2. Not so high SpA, and no access to quick recovery and has to rely on Volt Absorb by switching into electric types which is so predictable, either that or Rest.
3. Could get easily rekt by OU mons, since its in RU.
4. Total taunt bait since the opponent, if a good player, he might predict it and usually use Taunt. That or he's gonna switch into a counter.
5. Not that good movepool and not much type coverage either, so it relies on stalling. That or I underestimated it. Sorry poor fishy guy.
Here's a set from Smogon:
Lanturn @ Leftovers Ability: Volt Absorb EVs: 204 HP / 96 Def / 208
SpD Calm Nature
- Volt Switch
- Thunder Wave/Toxic
- Protect/Heal Bell
See? Its more of support instead of a sweeper set. There is a sweeper set, but I guess its more effective having a support set. Here is what it says on Smogon:
This is Lanturn's most common set in the RU metagame, functioning
mostly as a defensive pivot; Lanturn can come in on common special
threats, while also being able to grab momentum with Volt Switch. It
is able to check many of the prominent special threats in RU, such as
Moltres, Omastar, and Manectric. Scald is a great move, as its burn
chance allows Lanturn to weaken physical attackers that try to come in
on it. Volt Switch lets Lanturn switch out of Grass-types and default
to a proper teammate. Thunder Wave can paralyze fast Pokemon such as
Accelgor and Sceptile, making them ineffective for the rest of the
match. Toxic, however, allows Lanturn to wear down bulkier Pokemon
like Druddigon and Slowking. Protect allows Lanturn to scout moves and
gain Leftovers recovery; and works well with Toxic. Heal Bell is
another invaluable support move in Lanturn's arsenal, allowing it to
cure the team and itself from status.
The given EV spread allows Lanturn to avoid being 2HKOed by Moltres's
Hidden Power Grass, while still being able to check Entei and Emboar
relatively well. A Calm nature is chosen to maximize special bulk to
make checking Moltres easier. Volt Absorb allows Lanturn to come in on
Galvantula and Manectric, while giving it some form of recovery
outside of Leftovers. RestTalk is usable to provide Lanturn some form
of recovery, and can repeatedly check Moltres. This is, however, quite
situational otherwise. Ice Beam could also be used to hit Druddigon
and Grass-types, but Lanturn is too weak most of the time anyways.
Spikes support is useful because of the numerous switches Lanturn
forces; Ferroseed, Roselia, and Scolipede are all viable options for
Spikers and handling opposing Grass-types. Scyther can be a decent
teammate, as it can handle opposing Grass-types, and has U-turn to
form a VoltTurn core with Lanturn. Emboar and Entei are excellent
choices to handle Grass-types as well. Clefable and Alomomola are good
teammates to pass Wishes to Lanturn due to its lack of recovery.
Finally, Cryogonal is a great choice to remove entry hazards to
prevent Lanturn from being repeatedly worn down. Cryogonal can also
handle Grass-types decently for Lanturn, while Lanturn resists
Fire-type moves in return
Although this is for RU format, this is still how Lanturn works as a support. Some people do use Lanturn in Gen 5 OU, since it has a hige amount of bulk from its HP. In conclusion, Lanturn is not really a good mon in OU, but its also not that bad. The Smogon analysis even said it lacks recovery. Soooo, yeah, not that worth it. Chansey or Blissey is much better.
Hope this helps!