I read that running a full node provides "more security" than running a SPV client. What does this concretely mean? I think I understand pretty well how those two kinds of nodes work but I do not see what risks one takes running a SPV node. True a lightweight client cannot check by itself that unconfirmed transaction are valid. Is this the only difference as regards security? Even for a full node, accepting an unconfirmed transaction is not totally safe. I am asking this question because I try to understand what would be the effect of bigger blocks on the Bitcoin network. Therefore I need to understand why people choose to run full nodes/lightweight clients. I see very well why some people would choose to run SPV nodes but I don't understand why somebody would rationnaly chose to run a full node.
Thank you by advance!