Kanji radicals are important. They are like pre, pro, con, etc for the latin rooted languages. We, at lease myself, unconsciously reply on the knowledge about the radicals to relate to the rest of the character and remember it. So often that logical process helps remember the kanjis you haven't used for a long time but it's absolutely necessary to remember them in Japanese social life. So my answer is, it is OK to forget some kanjis but you will need to remember it anyway, in Japanese society. 

but like you mean the 訓読み reading of the radicals. i know how to write kanji but like is it necessary to know all the radicals 訓読み reading.