Telescopic poles are a must-have if you're heading into the backcountry or ski touring. The big advantage is adjustability—you can lengthen your poles for uphill skinning (where you want more reach) and shorten them for the descent or steep traverses. That versatility makes a real difference on variable terrain.
For resort skiers, though, telescopic poles are usually overkill. The locking mechanisms add weight and complexity, and they can occasionally slip under heavy pressure if not tightened properly. Fixed-length poles are simpler, lighter, more durable, and cost less—hard to beat if you're just lapping the lifts.
Where telescopic poles shine is backcountry versatility and travel convenience. They pack down smaller for luggage and can be shared between users of different heights. Just make sure to check and tighten the locks before each run to avoid unexpected collapse.