It turns out that the most important digits on your hands, when it comes to playing cello, are your thumbs. I base this on my vast 10 months of violoncello playing.
The right thumb is the spring that allows you to control the bow, particularly when playing rapid eighth or sixteenth notes. It the thumb is rigid or straight you lose flexibility and control. With the thumb relaxed and ever so slightly curved you can roll the bow (i.e., change the contact of the bow hairs and string from the edge of the hairs to the flat of the hairs), and you can quiver the bow in place to play very short, rapid notes.
Your left thumb is the pivot point around with your fingers are placed on the fingerboard. Ideally the thumb is opposite your middle or second finger. In pieces with backward extensions, necessary to play a Bb for example, moving your thumb as you extend causes you to lose a good first position location. Rooting the thumb as you extend backward keeps your first position placement so you are ready for the next note.
While the positions (first, second, third, et cetera) are determined by where the first finger is located, the real key is where your thumb is located. As you shift you need to move the thumb. Letting the thumb lag behind introduces tension in the hand and makes reaching the full width of the notes the fingers should span harder than necessary.
I find that when I concentrate on moving my thumb, or not moving, as required by the shift or extension being performed, that my intonation improves immensely. And it is easy to position my thumb (one digit) rather than my fingers (four digits). Plus, as you move up in pitch on the fingerboard, the placement of the fingers changes relative to each other. High on the fingerboard requires the fingers be closer together. It’s far less work to position the thumb, than to position all the fingers. This of course is only half true. You have to position the fingers regardless. However, being conscious of the thumb and letting muscle memory take care of the fingers seems to work better for me.