Should I generate and set these parameters?
Does it have any influence on [the] security...of ssl?
Yes, when enabling Perfect Forward Secrecy. An appropriate ciphersuite must also be configured.
If a future attacker compromises your TLS, with PFS past traffic they intercepted and retained still cannot be decrypted.
Generate a DHE prime no smaller than your SSL certificate RSA private key. Given a 2048 bit private key:
$ openssl dhparam -out dhparam.pem 2048
Generating DH parameters, 2048 bit long safe prime, generator 2
Does it have any influence on [the]...computational load of ssl?
Too little to worry about.
Google I/O 2014 had a good HTTPS Everwhere talk which covered these and related topics in a broad fashion.