What types of clients need a trademark?
Really, any client could use a trademark if they have any sort of branded product. A trademark identifies to a consumer or a user of a product or goods what the source of the goods or services is.
For example, if somebody picks ups a product on the shelf or sees something and they see your trademark associated with that product then they know it came from you from that client.
And, so, it’s really about brand protection for the client. The trademark identifies the brand and associates the maker or the owner of the trademark with those particular goods.