I was talking about (column-wise) saving each column in a separate binary file. If you need row-wise write, you can just store all table in one binary file row-by-row, and append new rows to its end.
Column-wise option is better and faster for analytics, since you can easily select individual columns without loading the whole table, while row-wise is better for data acquisition row-by-row (see also AoS vs SoA problem). Writing binary files is trivial and fast - no convertion to text is needed. Also, you may want to save metadata file with fieldnames and datatypes, along with binaries. BSON files can be slower and bigger, especially if you duplicate fieldnames for each row.
HDF5 is also very fast and space-efficient due to optional compression, and also supports chunking for incremental writes, you can start with it (actually, Julia and Matlab uses it to store variables to files).