Obviously spread is a deciding fact for determining the profits. Specially for traders who are doing short term trading. So for example if you are a short term trader and you trade 1 lot positions 5 times a day and take 5 pips on each entry on average in that case think of a broker like Exness who has low spread 1 pip spread vs 3 pips spread on eurusd brokers. In this scenario you are paying 2 pips extra to the 2nd broker and thats $20 per transaction and $100 for a day, $2000 a month and $24000 a year. I think now you have a fair idea about how important is the spread for short term traders. My broker Exness offers tightest spread in the market.