It only works vs. Forked Bolt. Most of your creatures still die to Bolts and Rough//Tumble and Firestorm also still are cards.
Also, when I have 4 mana left over I'd rather just go ahead and cast, say, Natural Order.
Now, the lifegain could theoretically, however slightly, help you in the Storm-MU's but running those in your SB means you'd have to skip on stuff that you'd usually fight Storm with so that's just filling one hole with another. Don't get me wrong - at some point in time I ran an
Essence Warden in my SB that would come in when facing Storm, and on occasion it even managed to save me from Storm once or twice, but there is a reason it doesn't have a spot in my SB anymore... Too often it does too little.