No stoploss could mean that the trailing will start instantly.
For example a trailingstop of 200 will put a stop at -200 and trail it along the way, immediately.
A stoploss, and a trailingstop, could mean that the trailing will start at break even.
In this case you can have for example a hard stoploss at -200 and a trailingstop of 50,
Then the trailing will start when price moves over the break even point.
Also there could be start, step, stop.
That's more advanced trailing where the trailing starts at a predefined level and then adjusts in step's of x pips and etc.
There are many variations on this, a noticeable one is the dynamic trailer which not only moves the stop closer,
but also moves it further away when spreads get out of control... In that sense it offers extra protection.
So it all depends on what you want to do.
I have a stop loss and a Trail but it only trails when it moves in a positive. I didnt have the trail stop only breaking above break even meaning it should trigger immediately under my sl) but it only moves when it moves in a positive.
I want a trail to work with a sl even when it is not breaking even.