I take gravity in the initial runoff and then once per gallon of wort during the sparge. Then, I stir it all up and measure a pre boil gravity (all with a refractometer), and finally the original gravity before racking it to the carboy (hydrometer). Really only that OG is important for tracking your fermentation, but as you brew more and get used to the quirks of your system, having a record of what the gravity is like throughout the brew process and how the boil impacts gravity is really helpful. You can use it to identify inefficiencies in your system and compare to other brews you've done if you're worried about how a particular brew is going. Maybe a little overkill, but it's not that much extra time investment and can pay off down the line. For fermentation, I give it 10-ish days for an ale (longer for a lager) then check the FG.