A ranger could have 4,000 mana and it really wouldn’t change what they can do. This is the biggest mana sink for a soloist challenge-type ranger. (Assuming you don’t just Ensnare and backpedal while plunking):
https://wiki.project1999.com/Ensnaring_Roots
For a SK or pally the questions are:
Did the sapper land?
Do you need to reproc avatar?
Are taps or HoT’s keeping up with incoming damage?
Are you mana neutral?
The last question is where the big mana reserves are make or break. Especially for a SK since the taps heal more/second than Celestial Cleansing but are mana intensive. A SK with a smidge over 2k mana can tap health 3040 back; with 3500 mana they can tap back 5070 health.