The only difference between these two trading is that, in spot trading is easily to monitor your trade but with convert form you can only place order and having lasting and limited period of 30 day thereabouts. Spots trading doesn't have lasting period and I believe can remain there as long you places your buy or sell order so whenever the market reaches your orders within 2 months or more it triggers automatically without expiration.
That is why people often use the spot trading and somewhat not too familiar with convert methods.