In Hyper Offense, there are 4 main roles I know of. They are the Hazard Setter, or lead, the Sweeper, the Wall Breaker and the Late-Game cleaner. Out of these, the only one that is reliably sacked is the Hazard Setter. This is usually the case because the only goal(s) of the Hazard Setter is to set up Hazards and (sometimes) to prevent the opposing Lead from setting up Hazards. Now, why it is usually sacked. In Hyper Offense, many of these Offensive Presence are very frail, which of course lessens the desire to switch-in unless one is absolutely certain that they can switch-in safely(e.g. The opponent will also switch, immune to status move, etc.). Due to this, These main 4 roles have developed to take On all types of roles in the Meta. There are only a few cases I can think of when to sacrifice something, especially in Hyper Offense from experience( Yes Swastik, I do play Hyper Offense sometimes). They are as follows.
When no member of your team can safely switch-in (e.g. Due to the presence of no members to successfully absorb a certain Status move)
Having the advantage and not wanting to take damage due to the frailty of your Sweepers. This is my most common scenario I run into when facing something, especially bulky tanks.
Like sumwun said, there is also the case of being willing to sacrifice because you know you can check/counter the rest of the opponents team.
These are mainly the only cases I can think of (Comment if you know any more), that would lead to you having to sack your team members. Just like Prof. Said, it is usually ok to sack some team members when your lower in the ladder, but once you get higher, it is best to preserve them to allow them to deal as much damage as possible due to the better teams and decision making of those players.