When a crash helps the arrangement
Give each crash a musical reason and listen to what follows it.
A crash can mark an entrance, reinforce a band accent or begin a sustained cymbal texture. The question is whether that sound supports this part of the arrangement. There is no useful crash limit that fits every song.
Listen before marking the chart
Listen through the recording the band is using and mark the entrances where the drums clearly change. Notice whether a crash joins a vocal entrance, answers it, or rings during an instrumental passage. Check which of those choices the live arrangement keeps.
At rehearsal, compare one transition with and without the crash. Keep the groove otherwise the same. Ask whether the entrance became clearer and whether the following lyric stayed audible.
Practice the hit and return
For a simple exercise, play three bars of a 4/4 groove and crash with the kick on 1 of bar 4. Return to hi-hat eighth notes on the & of 1. Count through the crash bar and the following groove bar, keeping the pulse going after the accent.
Listen for one combined attack on the crash and kick, then steady time afterward. A late return usually needs a slower repetition or a more reachable cymbal position.
Decide how long it should ring
Let the cymbal sustain when the arrangement calls for an open entrance. For a sharp band stop, agree whether to mute it and when. Rehearse that ending separately; a cymbal still ringing may undo an otherwise clean cutoff. If the crash covers the next line, try a gentler strike or another cymbal sound before changing the whole groove.