I use Electrum on my laptop but also keep a full node 24/7 on my home server that will hopefully keep me from connecting to a cancer node. So please don't answer with that scalability simplified payment verification client block height vs. depth crap. It's a simple question.
What's a "cancer" node?
Backfilling the network with clients controlled by an attacker. The attacker nodes are called cancer nodes. Always up full nodes create constant connections that resist this type of attack. If the attack network was large enough clients starting up briefly to only make one or two transactions may only connect to cancer nodes. This would effectively create two networks. Thin clients are booted up briefly to perform transactions then closed. Too many thin clients supporting the network (running briefly and closing) create an environment for this attacks success. I run a full node 24/7/365 to ensure I always connect to the "real" network.