If a drug is lipid soluble, it does not have to rely on transport proteins or pinocytosis to enter the target cells. This is faster, allowing for simple diffusion to be exploited.
A higher lipid solubility gives faster uptake and reduces the probability of ionic trapping.
Individuals with higher proportions of body fat may have the drug build up (or form a reservoir) within body fat. This can cause issues, reducing the effect of the drug, and so must be taken into account while prescribing. To contrast, individuals with very little body fat will have much greater variability in the concentration of the drug, due to there not being a reservoir present in body fat. This must also be taken into account. As body fat is lipid based, drugs that are very lipid soluble will be more prone to accumulate in body fat, while those that are less lipid soluble will be less affected by this issue.
Lipid solubility influences the pharmacokinetic profile of a drug, due to the concentrations observed becoming more variable with more lipid soluble drugs.