Starter liquid

I have read that you are supposed to dump most of the liquid from a starter and leave just enough to make a slurry but is there anything wrong with dumping all the liquid in there?

For me it depends on the size of the starter and how long I have allowed. 1 liter or less goes straight in. 1L to 2L is decanted if I have allowed time. More than 2L would put off brew day so I could decant. If I don't decant I pitch at high krausen, about 18-24 hours on the stirplate.

Slightly off topic, but try this: pour the starter beer into mason jars or beer bottles and put them in the fridge. There's enough yeast suspended in there to make a starter for your next batch.

I think if you decant the liquid off the starter, much of the less floculant (and higher attentuation) yeast will be separated from the rest. This changes the characteristics of your yeast population, especially over several generations. I'd say take a cell count of the liquid you wish to remove, if you have a reasonable amount then you altered the population characteristics. Especially if there is enough yeast in suspension to start another batch, then you have created two very different results. One beer will come out dryer and less clear than the other. I guess some worry about the additional fermentation byproducts that you can smell in the starter, but it should not make a big difference, yeast reabsorb a fraction of what they emit, more so the less flocculent they are (in general). So by losing the less floculent fraction of the population you lose a part of the yeast's ability to reabsorb the by products - but then you added more so I guess it depends on yeast? I'd say throw it all in.