Good point about pruning, I forgot that it was recently implemented. However, I'm fairly sure that even with Bitcoin Core running a pruned blockchain, you'd be using more disk space than just running Electrum (plus you'd have to sync up the blockchain everytime you'd want to send a transaction if the computer isn't being used as a full node).
That can be a nuisance, but it is the price of privacy and security.
As for the extra load on the network, I meant that 30-40GB of bandwidth would be required to download the entire blockchain. I'm sure some full nodes are hosted on VPS' with limited bandwidth. Why use up bandwidth on these VPS full nodes if it isn't needed by using a wallet such as Electrum?
Those VPS nodes probably aren't accepting incoming connections. The DNS seeder will usually only hand out node's that have had a high uptime and thus most likely have a high bandwidth.
Also, Electrum connects to specific Electrum servers, not random full nodes. Those servers are run by volunteers.
Regarding the full node argument, I agree that more full nodes on the network is always a good thing, but the OP hasn't specified what sort of uptime their computer has. I wouldn't assume that their computer on enough to be a full node (nodes need to be on for at least 6 hours or so to be considered a full node IIRC). Additionally, we don't know if the OP has any sort of bandwidth limitations. If they do, running a full node probably isn't the best idea.
There is no time requirement to be a full node. A full node is any node that fully validates and verifies every single block and transaction it receives. Thus any time that Bitcoin Core is run, the computer is a full node.