Hi, the problem is that all these unbalancing forces can be cancelled out by trim tabs and/or uniform loading (e.g. having two people in a twin seater.) However the balance only occurs for one set of conditions... Alter anything and the plane will no longer fly hands-off. The two examples I can quote are as follows...
During my QXC in a Tomahawk I was obviously flying solo and the weight of just me in the LH seat made the plane pull to the left quite a lot. After the first landing I moved my heavy pilots case from the back to the RH seat, and that made some improvement.
The second example is a C172, this is rigged to climb at full power without hardly any rudder requirement when two up. However in the cruise at the lower power setting, the rudder trim needs setting two notches to the left to centralise the ball... This in turn requires a slight amount of right aileron to stop the resulting turn.
One further factor is that fuel can migrate from one tank to the other if the fuel selector is set at 'Both'. If the wings are not level, the condition can get progressively worse, as fuel transfers to the lower tank, and it also does not help if you park with one wheel in a hollow. Also some aircraft without a 'Both Selector' only use fuel from just one tank at a time.