There is plenty of information about DNSSEC on the web, and there are no straight answers to your questions, but know that:
- DNSSEC is an extension to the DNS protocol supposed to be backward-compatible: it means, if you do not change anything, you won't probably even feel the difference
- the purpose of DNSSEC is, in a few words, to make a client trust a DNS reply coming from any DNS forwarder; if you don't want/use it and you are concerned about security, it will make a BIG difference (because cache poisoning is possible)
From a user point of view:
- if a client you use wants DNS replies with DNSSEC activated (this will eventually become a standard, otherwise DNSSEC loses its purpose), know that some routers are incompatible and queries will fail until you change/upgrade it
From a hoster point of view:
- if one of your DNS customers creates a key and wants to use DNSSEC for his domain, you won't be able to accept his request because DirectAdmin doesn't manage it, and worst of all it will eventually overwrite the zone file if you do it manually